A molding apparatus 1 having a structure as shown in FIG. 8 has been conventionally used for forming molded objects corresponding to, for instance, CDs, LDs and the like optical disks. The molding apparatus 1 of this type is roughly comprised of a nozzle 2 for injecting a plasticized molten resin to form molded objects, a fixed mold 4, and a movable mold 9. A cavity 12 into which the molten resin is injected to mold an object is formed between the fixed mold 4 and the movable mold 9.
The fixed mold 4 has a sprue bush 6 fitted thereto. The sprue bush 6 includes a recess part 13 into which the nozzle 2 can be inserted and removed, and a sprue part 7 for communicating with the recess part 13 and the cavity 12. The sprue bush 6 is positioned relative to the fixed mold 4 by being fitted at an inner circumferential face 5a of a locating ring 5 set to a fixed plate 3. The sprue part 7 is designed to be concentric with the locating ring 5 and the nozzle 2 when the sprue bush 6 is fitted in the locating ring 5.
Meanwhile, the movable mold 9 has a stamper 15 which is installed facing the cavity 12 and on which data to be transferred to the molded object are formed.
In the molding apparatus 1, for injecting the plasticized molten resin into the cavity 12, the nozzle 2 moves down and comes into contact with a contact face 6b of a bottom part 6a of the sprue bush 6, whereby an injection hole 2a of the nozzle 2 communicates with the sprue part 7. The plasticized molten resin is injected from the nozzle 2 by a plunger (or screw). This injected molten resin is injected via the sprue part 7 of the sprue bush 6 into the cavity 12. Pits and projections constituting the data of the stamper 15 are thus transferred to the molded object.
For releasing the molded object from the movable mold 9, simultaneously with when a mold opening operation is performed by driving the movable mold 9 after the resin is injected, air is blown to the molded object from a path 10 formed in the movable mold 9. Ejection of the sprue part 7 and the molded object is performed after the movable mold 9 is completely opened, with the air being simultaneously blown to the molded object from the path 10, thereby separating the molded object from the movable mold 9. The molded object is transferred to outside of the molding apparatus by a take-out apparatus after this separation is finished.
The conventional molding apparatus 1 of the above structure has problems as follows. Specifically, the stamper 15 and the molded object relatively tightly adhere to one another because of the molding operation performed for creating a molded object. As indicated in the right half of the movable mold 9 in FIG. 8, the stamper 15 is held to the movable mold 9 in a manner so that an inner circumferential part 15a and an outer circumferential part 15b of the stamper are caught by the movable mold 9. After a mold opening operation is performed after molding, as shown in FIG. 9, an ejector pin 11 projects from the movable mold 9, whereby the molded optical disk 16 is pushed up towards the fixed mold 4, and the optical disk 16 and the stamper 15 are separated from each other.
In an event that a middle part, between the inner circumferential part 15a and the outer circumferential part 15b in a diametrical direction of the stamper 15, is not released from the molded object 16 when the mold opening operation is performed, the stamper 15 is deformed so as to float away from a central part of the movable mold 9 as indicated in the drawing. The larger an angle θ 1 between a data transferred face 17 of the molded object 16, to which the data of the stamper 15 are to be transferred, and a data forming face 18 of the stamper 15, having pits and projections corresponding to the data, the more projection parts of the data forming face 18 rub side faces of projecting parts formed on the data transferred face 17, thereby deforming the data transferred face 17. There is a problem in that data cannot be correctly formed on the molded object 16 in consequence of this deformation, resulting in quality deterioration of the molded object in some cases. More specifically, deformation of the data transferred face 17 appears as a whitish phenomenon or a so-called jitter in a ROM (read only memory) when the ROM is constituted of the optical disk, and data is written exceeding an allowable range in a RAM (random access memory) when the RAM is constituted of the optical disk.
In the stamper 15, as described above, since the projection parts of the data forming face 18 are rubbed and worn, frequent replacement of extremely expensive stampers 15 becomes necessary to eliminate the above problem of the molded object and to maintain quality of the molded object, which leads to an increase of costs.
The present invention is devised to solve the above problems and has for its object to provide an optical disk molding apparatus and method which can prevent deterioration in quality of molded objects.